The present invention relates to a rapping shaft device assembly for electrostatic precipitators and more particularly relates to an isolator which is rotatably mounted and includes heat means therein, the support means for the isolator including a roller which has minimal contact with the isolator thereby minimizing the heat transfer from the isolator to the support means.
Electrostatic precipitators are provided with discharge and collecting electrodes which attract particulate matter from contaminated air streams passing therethrough. Particulate matter or dust which piles up on these electrodes must be removed by shaking or washing of these electrodes. Normally, the shaking is accomplished by vibrators or rapping devices. Generally, such devices have a rotating shaft with tumbling hammers fixed thereto and each of the hammers strikes a rapping rod linked to one or more discharge or collecting electrodes so as to shake or vibrate them. When the electrodes are under high tension, the rapping shaft must be isolated electrically from the drive outside the precipitator casing. Normally, this isolation is accomplished by an electrically isolating link which joins the hammer shaft and drive shaft together in one link. Inevitably, the isolator is placed inside the casing in the dust laden gases. Thus, part of the dust settles continuously upon the isolator and when the dust layer is wet by condensation of vapors, the high tension potential causes creeping currents or even flash overs thereby cracking the isolators. However, in order to prevent the vapor build up on the isolators the most common means of preventing this condensation build up is to heat the isolators so that the dust remains dry. This heating of the isolator can be made from outside by a heating element which reaches into a cavity in the isolator from the driving end or by heating the incoming air to the casing thereby keeping the environment within the casing at a temperature above the condensation point of the vapors which are passing therethrough. However, many difficulties have arisen in relation to gas temperatures in the range of 150.degree. to 500.degree. C. Firstly, the heat from inside the casing will be conducted by the isolator to the bearing of the isolator cap. When the bearing is heated up to 150.degree. C. or more, the lubricant will dry out, solidify, eventually carbonizing and jamming the cap to the bearing. In order to alleviate this problem the driving means have been electrically insulated from the rapping shaft by means of intermediate insulated couplings. Examples of these devices are noted in U.S. Pat. Nos. 2,864,459 and 3,173,773.